The rate of de novo galactose synthesis in patients with galactose-1-phosphate uridyltransferase deficiency

Using both a continuous infusion of isotopically labeled [1- 13C]galactose with a steady-state analysis and a single injection kinetic approach, we have calculated the apparent galactose appearance rate (GAR) in patients with galactose-1-phosphate uridyltransferase deficiency and control subjects. With the steady-state protocol, the GAR in 18 patients less than 18 years of age was 1.34 ± 0.53 mg/kg/h (mean ± SD) and was significantly greater than the mean of 0.56 ± 0.01 mg/kg/h ( p=0.004) in five patients above 18 years of age. Patients who were given a priming dose of [1- 13C]galactose had a reduced GAR compared to those without a priming dose, 0.73 ± 0.05 ( n=9) vs 1.46 ± 0.62 ( n=14) mg/kg/h ( p=0.005). The GAR in controls was lower than in patients ranging from 0.58 to 0.68 mg/kg/h in children and 0.07–0.09 mg/kg/h in adults. In the single bolus studies the plasma [ 13C]galactose enrichment decreased in a biexponential pattern suggesting at least a two-compartment system. The calculated GAR in three adult patients was similar to that found in them by the continuous infusion technique. The GAR in patients suggests the source of galactose for the continued elevation of galactose metabolites as well as the basis for the long-term complications in galactosemia despite restricted dietary galactose intake.